The physicochemical, UV-induced surface modifications to silica nanoparticle (SiNP) - epoxy composites have been investigated. The silica nanocomposites (SiNCs) were prepared using a two-part epoxy system with 10 % mass fraction of SiNPs and exposed to varying doses of high intensity, UV radiation at wavelengths representative of the solar spectrum at sea level (290 nm ‹ 400 nm) under constant temperature and humidity. Visibly apparent physical modifications to the SiNC surface were imaged with scanning electron microscopy. Surface pitting and cracking became more apparent with increased UV exposure. Elemental and surface chemical characterization of the SiNCs was accomplished through energy dispersive X-ray spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS), while attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) revealed changes to the epoxy‰s structure. During short UV radiation exposure periods, there was an increase in the epoxy‰s overall oxidation which was accompanied by a slight rise in the silicon and oxygen components and a decrease in overall carbon content. The initial carbon components (e.g. aliphatic, aromatic and alcohol/ether functionalities) decreased and more highly oxidized functional groups increased until sufficiently long exposures at which point the surface composition became nearly constant. At long exposure times, the SiNC‰s silicon concentration increased to form a surface layer composed of ≈75 % silica (by mass).